Nominally undoped layers which had been grown by molecular beam epitaxy were investigated by using temperature- and frequency-dependent admittance spectroscopy. The space-charge region, which was required for the detection of deep defects, existed only at low frequencies and deep-level transient spectroscopy measurements therefore failed for this material. Two deep defect levels were identified in molecular beam epitaxially grown layers. The thermal activation energies were 0.45 and 0.63eV. These deep traps were well known from deep-level transient spectroscopic and thermally-stimulated conductivity measurements of metalorganic vapor-phase epitaxially and hydride vapor-phase epitaxially grown GaN.

Analysis of deep traps in hexagonal molecular beam epitaxy-grown GaN by admittance spectroscopy A.Krtschil, H.Witte, M.Lisker, J.Christen, U.Birkle, S.Einfeldt, D.Hommel: Journal of Applied Physics, 1998, 84[4], 2040-3